2D polynomial fit of the ET1 line centroids in slice 10 of MRS sub-band 1C. The scatter points show the ET1 centroids fitted on the detector (x, y) pixel space. The respective wavelength values matched using the FTS data are shown on the z-axis and in the color scale of the dots. The x and y axes show the respective pixel coordinates on the detector plane. The light blue plane shows the fitted 2D polynomial.